As people have already said you gain speed by dropping down the steepest part of the wave. As you take off turn off the bottom and then look down the line and look for the steepest part of the wave you need to climb and drop in a flowing motion across this section.
As you climb this steep bit you should try and unweight yourself make yourself go light and then as you drop back down make yourself go heavy. Sounds wierd but practise makes perfect. You need to this very smoothly though. I have seen paeople trying to climb and drop accross the fgace with there arms failing like pendulems and their bodys twisting wildly. This is a very crap way to do it and you will notice they are not gaining any speed at all. Watch a good guy and you will see that they seem to use the whole face and they gain so much speed its incredible. it takes a lot of prcatice but if you keep things smooth you will gain a lot of speed.
Backhand is another matter though you have to use your body more but you should be able to gain as much speed.
When your in a flat section instead of pumping and boucing your way through it (which looks Fugly) try and weave bouce like tik tacking on a skate board it looks better and is a lot more function at maintaining and gaining speed. USe you trailing arm as well bring it around on cutbacks and turns its aheavy bit of pink stuff that really helps to bring that board around. Also you should have a an arm in the water during most maouvers watch a surf vid and study the pros they use an arm in the water as a pivot point. Anyway thats enough tips from me. If we ever compete against each other your gonna know all my secrets!!